Golf balls can generally be divided into two classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by tensioned elastomeric material, and a cover. Solid balls have traditionally been considered longer and more durable than wound balls, but also lack the particular “feel” that is provided by the wound construction and typically preferred by accomplished golfers.
By altering ball construction and composition, however, manufacturers can vary a wide range of playing characteristics, such as resilience, durability, spin, and “feel,” each of which can be optimized for various playing abilities, allowing solid golf balls to provide feel characteristics more like their wound predecessors. The golf ball components, in particular, that many manufacturers continually look to improve are the center or core, intermediate layers, if present, and covers.
The core is the “engine” of the golf ball when hit with a club head. Generally, golf ball cores and/or centers are constructed with a polybutadiene-based polymer composition. Compositions of this type are constantly being altered in an effort to provide a targeted or desired coefficient of restitution (“COR”) while at the same time resulting in a lower compression which, in turn, can lower the golf ball spin rate, provide better “feel,” or both. This is a difficult task, however, given the physical limitations of currently-available polymers.
Manufacturers also address the properties and construction of golf ball intermediate and cover layers. These layers have conventionally been formed of ionomer materials and ionomer blends of varying hardness and flexural moduli. This hardness range is still limited and even the softest blends suffer from a “plastic” feel according to some golfers. Recently, however, polyurethane-based materials have been employed in golf ball layers and, in particular, outer cover layers, due to their softer “feel” characteristics without loss in resiliency and/or durability.
One conventional material that has been used to form golf ball covers is balata, a natural or synthetic trans-polyisoprene rubber. The softness of the balata cover allows the player to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots. However, balata covers lack the durability required by the average golfer, and thus are easily damaged. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata covered balls, while also providing a golf ball with a higher durability and overall distance.
Ionomer resins (e.g., copolymers of olefin, such as ethylene, and ethylenically unsaturated carboxylic acids, such as (meth)acrylic acids, wherein the acid groups are partially or fully neutralized by metal ions) have also been used as golf ball cover materials. Ionomer covers may be virtually cut-proof, but in comparison to balata covers, they display inferior spin and feel properties.
Thermoplastic materials are used in golf ball applications, particularly because they are easy to implement and have high performance qualities at ambient temperature. They are also flexible and have a high degree of mechanical resistance. Nevertheless, thermoplastic materials have the drawback of low physical resistance to heat such that the products obtained from said materials have, depending on their use, a short service life. On the other hand, materials known as “thermosetting” materials are difficult to shape, thus even though they may be heat resistant, their use is limited.
Methods have been formulated to form thermoset polyurethane and polyurea materials for use in golf balls. In order to achieve this, the preparation of a thermosetting polymer has been proposed by modifying easily processed thermoplastic polymers to enable the finished product to be cross-linked. One popular method is the reaction of thermoplastic polyurethane or polyurea compositions with a toxic isocyanate monomer like MDI or TDI to create a cross-linking moiety. This is usually achieved by achieved by mixing and extruding a polymer, particularly a polyethylene with a peroxide. However, this type of method not only has the drawback of being possible with only a limited number of polyethylenes, but also of requiring very expensive industrial installations.
Other methods include the use of a high energy radiation to produce a cross-linked TPU, such as irradiating a polymer with doses measuring 80 to 200 KGy. It should, however, be noted that this type of treatment is very expensive and also tends to deteriorate rather than improve the polymers used.
Hebert, et al., U.S. Pat. No. 5,885,172 (“the '172 patent”) discloses a multilayer golf ball giving a “progressive performance” (i.e. different performance characteristics when struck with different clubs at different head speeds and loft angles) and having an outer cover layer formed of a thermoset material with a thickness of less than 0.05 inches and an inner cover layer formed of a high flexural modulus material. The '172 patent provides that the outer cover is made from polyurethane as described in Wu, et al., U.S. Pat. No. 5,692,974, or thermoset polyurethanes such as TDI or methylenebis-(4-cyclohexyl isocyanate) (“HMDI”), or a polyol cured with a polyamine (e.g. methylenedianiline (MDA)), or with a trifunctional glycol (e.g., N,N,N′,N′-tetrakis(2-hydroxpropyl)ethylenediamine). The '172 also provides that the inner cover has a Shore D hardness of 65 80, a flexural modulus of at least about 65,000 psi, and a thickness of about 0.020 0.045 inches. Exemplary materials for the inner cover are ionomers, poly-urethanes, polyetheresters (e.g. HYTREL®), polyetheramides (e.g., PEBAX®), polyesters, dynamically vulcanized elastomers, functionalized styrene-butadiene elastomer, metallocene polymer, blends of these materials, nylon or acrylonitrile-butadiene-styrene copolymer.
Therefore, a continuing need remains for novel golf ball construction, and particularly for a golf ball cover that has the desirable and/or optimal combination of performance characteristics, while also having good abrasion durability, feel, and friction characteristics that result in favorable spin. The present invention is directed to golf balls having components formed of novel poly(dimethyl siloxane) (PDMS) ionomers.